I'm with SiN on this one. I love the things. I was kinda pissed when I learned my uni. didn't allow them. They are considered a fire hazard along with lavalamps and George Foreman grills. We can have toasters and coffemakers, but a blacklight is considered contraband. I'm not taking a risk with one. Kinda hard to remove from the wall when we have room inspections. An electric grill on the other hand can be stuck or hid just about anywhere.
Another thing that reacts well is highlighter fluid. You can scribble all over just about anything with a yellow one and people can't tell. Test a spot before you go all willy-nilly, though. Also, keep in mind that a fresh coat of paint may not keep it from showing up under a UV light.